Generally, it has been practically important in view of the increase in value of waste resources and of avoiding environment contamination that valuable metals are recycled from scraps from electronic device such as a print circuit board used for various electronic products, or from waste catalyst that comes mainly from a chemical factory. Further, because of the amount of heavy metals contained in waste water from a plating factory or clothing factory, etc., or waste water produced when developing photographs, it is important in view of the increase in value of waste resource and of avoiding environment contamination that the waste water is recycled and the valuable metals are recovered efficiently.
As for a method for treating waste water containing Pt, Rh, Au, Ag, Cu, etc., and recovering them, it has been proposed that the waste resource is crushed and then leached with a solvent of acid or alkali, etc., and valuable metals are obtained using a chemical precipitation method or electrolysis method. The electrolysis method is used partly not only when recovering the valuable metals or heavy metals contained in waste water but also when treating or producing general inorganic compounds or organic compounds. However, there are drawbacks in that treatment time is long and efficiency is low using existing electrolytic equipment and further it occupies a large space.
The existing electrolytic equipment for electrolysis resultant product within waste water and obtaining final product is configured generally such that anodes and cathodes of a parallel plate type are arranged alternatively within an electrolytic bath. Under this type of an electrolytic bath, material is moved through only diffusion and thus the solution is compulsively convective through stirring or gas injection to increase material movement velocity. However, there is a limitation electrolysis condition of a high current density. This electrolytic bath may be configured as a rectangular shape or column shape depending on necessity thereof.
Referring to a waste water treatment method used in a current plating industry, the waste water is mainly slugged with a chemical agent and buried in the ground. Valuable metal components within the waste water and industrial water are not recycled but are discharged outside, causing serious environmental contamination and incurring the cost of treating them with the chemical agent.
FIG. 1 shows electrolytic bath 100 according to one embodiment of a prior art for electrically depositing and recovering valuable metals from plating waste water or waste water containing valuable metals, wherein cylindrical internal electrode plate 130 and cylindrical external electrode plate 120 are arranged inside cylindrical housing 110 within which internal cavity 113 is formed. Inlet 112 and outlet 111 through which waste water is inputted and discharged are formed in housing 110.
Through the above configuration, electric power is supplied from an external power source (not shown) to internal electrode 130 and external electrode 120 and then current is applied thereto. At this time, the polarities of internal electrode 130 and external electrode 120 may be arranged arbitrarily wherein one assumes the negative and the other assumes the positive.
From the above polarities of the electrodes, electrons are supplied to the cathode from the power source and cations in the waste water (solution) within the electrolytic bath are diffused to a surface of the cathode wherein an electrochemical reaction occurs, that is, the cations receive electrons and are reduced to deposit valuable metals on the cathode and recover them.
However, according to prior electrolytic bath 100 having one cathode and one anode, since the specific surface area of the cathode is not large, the contact area between the waste water in the electrolytic bath and the cathode is small, and the contact time is short, causing the valuable metals to not be recovered efficiently. In addition, referring to a low concentration of the waste water, that is, the waste water contains valuable metals of 10 ppm or less, since the contact specific surface area is very small, depositing and recovering the valuable metal is difficult, causing the efficiency of deposition and recovering to be low.
In other words, since the reduction process occurs on a surface of a simple cathode, there arise problems in that reaction speed is limited and thus several electrolytic baths 100 are necessary for achieving mass production, and further that electrolysis efficiency decreases significantly as time passes.
Meanwhile, generally titanium (Ti) is used for the electrode plate material because Ti has the advantage of not being dissolved in the aqua regia used for recovering the valuable metals. However, Ti has low electric conductivity and thus other metal having high electric conductivity or a combination thereof is plated to a surface of the Ti electrode plate.
Additionally, an electrode plate of a dish sponge configuration which increases the specific surface area on which the valuable metals are electrically deposited and recovered has been used as the cathode, however, the cathode of the dish sponge configuration is fabricated such that a shape thereof is fabricated with a polymer compound (plastic) and then the surface thereof is coated with a metal having high electric conductivity such as copper (Cu) in order to increase electric conductivity, causing fabrication of a cathode of the dish sponge configuration to be difficult.
In addition, when the electrodes surfaces are coated with high electric conductivity metals, the coating metals are dissolved by additions (citric acid, cleaning agent, etc.) which are inputted during the electrolysis process in order to recover the valuable metals and then are extracted as impurities, causing overall electrolysis efficiency to be lowered.
Furthermore, the waste water which is inputted into the electrolytic bath 100 assumes a neutrality, acidity or alkalinity property depending on their characteristic properties and the metals plated on the surface of the electrode are dissolved depending on the pH of the waste water inputted into the electrolytic bath 100, causing the electrolysis efficiency to be lowered. As a result, these electrodes are not able to be recycled after recovering the valuable metals one time and thus have to be replaced. Accordingly, there is a need for an electrolytic bath in which the specific surface area in contact with the waste water is enlarged and through which electrolysis efficiency for recovering the valuable metals is increased.